This invention relates to earth drilling, such as for the installation of pipes, electrical conduits and the like. In particular, it relates to cleaning and recycling of used drilling slurry or mud, for recycling of liquids for re-use in the drilling process.
Drilling muds and slurries such as Bentonite-based mud are used in various earth drilling operations such as drilling and back reaming of passages for the installation of pipes, electrical conduits and the like. During the drilling operation, slurry may be used for high pressure jetting (cutting), cooling down of instrumentation, forming a wall cake, and carrying waste material out of the hole. The returned mud is typically captured temporarily in a lined pit for disposal or cleaning. Due to environmental concerns relating to used mud and the costs associated with Bentonite, as well as potential difficulties in obtaining water on the job site, it is advantageous to process the returns for re-use, by cleaning the used slurry of larger particulates such as rock chips and sand and recycling the resulting liquids. Cleaning is also required in order to prevent wear and damage to high pressure pumps, mud motors and the like which may be caused by sand or grit in the re-used slurry.
Bentonite in its refined form is a dry, mined clay which is typically supplied in the form of a fine powder. Bentonite and other similar slurry-forming powders resist mixture with water to form a well-mixed slurry. Mixing apparatus such as that disclosed in U.S. Pat. No. 5,779,355 (Pullman) may be used to efficiently produce a well-mixed drilling slurry.
The supply of a clean (i.e. free of larger particles) and well-mixed supply of slurry is critical for drilling operations. It is also desirable to provide a reliable apparatus for reliably cleaning used slurry from recycled slurry.
Various systems have been used in the drilling industry, and as well have been proposed in a number of patents for recycling slurry liquid. Typically, these employ various combinations of shaker beds and screens to remove the larger debris, and cyclonic cleaners to remove finer particles. Most also use two or more storage tanks to hold dirty and cleansed fluid, as well as a mixing system to restore the cleansed slurry to a reusable condition, for example by adding new Bentonite or other slurry-forming powder. Typically Bentonite is lost in the cleaning process and thus it is necessary to supply additional Bentonite to restore the drilling mud.
Arrangements for recycling drilling slurries proposed previously include U.S. Pat. No. 5,853,583 (Shah) which uses three holding tanks to hold partially cleaned slurry, and a combination of filter screens and cyclones for removing particulates. After removal of solids, the resulting liquid is discharged from the apparatus.
In another arrangement, namely U.S. Pat. No. 2,941,783 (Stinson), recycled slurry is filtered through a screen and cyclone, and then passed through a storage tank. Cleaned fluid is removed from the tank, and redirected back into a drilling stand pipe or the like.
It is desirable to provide an efficient and compact unit that may be readily transported to a drilling site. In order to provide a simple and effective apparatus and process for recycling drilling mud, it is desirable that the arrangement employ only a single tank, and not require a separate and additional mixing system for restoration of the recovered and cleaned liquid. This permits a compact, transportable unit for recycling liquid from used drill slurry. Thus, it is desirable to provide an effective and efficient filtering means, as well as mixing means within the tank to enable the system a clean source of useable drilling mud.
In one aspect, the invention is an apparatus for cleaning and recycling slurry such as well-drilling slurry or mud, comprising:
an inlet for receiving a supply of drilling slurry contaminated with particulates;
first screening means for coarse filtering said slurry;
a slurry tank, with mixing means within said tank for mixing slurry filtered by the first screening means;
an outlet conduit for discharging slurry from said tank;
a cyclonic separator for separating said slurry received from the tank into a first stream containing relatively coarse particulates, and a second stream containing relatively fine particulates;
a second, fine, screening means for receiving said first stream and removing particulates therefrom, and discharging the resulting screened fluid into said tank;
a discharge conduit for receiving said second stream from said cyclonic separator, and directing said stream back into said tank, and into a discharge outlet for re-use for forming a usable-slurry;
pump means for cycling said slurry through said system on a continuous basis; and
control means for controlling the operation of said system.
The cyclonic separator may comprise a bank of cyclonic separators operating in parallel.
Preferably, the second, fine, filter is positioned directly over the first filter means, which in turn is positioned over the tank. Thus, the filtered liquid flowing through the second screening means is discharged onto the first screening means and thereby assists in the screening process carried out by the first screening means. The first and second filters may be both mounted to a common frame for vibration by a single drive means. In another desirable aspect, the mixing means within the tank consists of a jet agitator, which directs one or more jets of liquid into the tank. The source of the liquid is drawn directly from the outlet conduit leading from the tank, thereby recycling a portion of the slurry through the tank.
In a further desirable aspect, the discharge conduit from the pump goes to a manifold for directing the partly cleansed liquid into several conduits. A first conduit leads to the cyclonic separator. A second conduit leads to a washing wand, which maybe manually operated, for cleaning of the screening means and other components of the apparatus. A third conduit may lead back to the inlet conduit, for increasing the liquid content of the incoming contaminated slurry, for improving the initial filtering operation.
The discharge conduit leading from the cyclonic separator may discharge the second, cleansed stream into an open trough having a first outlet for discharging liquid from the system and a second outlet leading back to the tank. The second outlet may be positioned above the first outlet to permit excess fluid to be directed back to the tank for recirculation.
Use of this apparatus provides a means for continually circulating the slurry through the mixing tank and various filtering and cleaning stages. Slurry removed from the system may thus have been recycled through the system several times.
In another aspect, drilling slurry is prepared by combining recycled liquid as processed in the above with Bentonite or other slurry-forming powder. In this aspect, a liquid stream exiting the cyclonic separator discharges recycled liquid into a shearing-type mixer as described in U.S. Pat. No. 5,779,355. Cleansed liquid is drawn into the mixer and combined with Bentonite powder in the shear mixer apparatus, to provide a supply of fresh drilling mud prepared at least in part from recycled liquid.
In another aspect, the invention comprises a method for cleaning well-drilling slurry contaminated with particulates, and restoring the slurry to a substantially new condition. The method comprises the steps of:
providing a source of contaminated drilling slurry;
discharging said contaminated slurry onto a first screening means;
screening of said slurry with said screening means, into a mixing tank;
mixing said slurry within said tank;
discharging partly cleansed slurry from said tank via a conduit, into a cyclonic separator;
discharging from said separator a first stream of slurry containing relatively course particulates, and a second screen containing fine particulates;
depositing said first stream onto a second screening means and screening out particulates from said first stream, said screened liquid being deposited into said mixing tank;
selectively directing said second stream from the cyclonic separator, whereby the second stream is either discharged from the system for re-use, or returned to the mixing tank for circulation through the system.
In a further aspect, the second screening means is positioned directly over the first screening means, and the screened liquids flow onto the first screening means to assist in the screening operation carried out by the first screening means.
In a further aspect, a portion of the at least partly cleansed liquid is withdrawn downstream of the mixing tank and piped into the source of raw slurry to facilitate the initial screening step.
In a further aspect, partly cleansed liquid is withdrawn for use in cleaning components of the cleaning apparatus.
In a still further aspect of the method, partly cleansed liquid is withdrawn downstream of the mixing tank, and is redirected back into the mixing tank via a jet cleaner, to provide the mixing means within the tank.